Indicating the passing of a projectile through an area in space

ABSTRACT

A method of and apparatus for indicating the passing of a projectile through an area in space comprising inciding the whole of said area with a projectile light beam and detecting a reflection of said beam off a projectile passing through said area resulting from incidence of said beam thereon thereby determining that said projectile passed through said area.

D United States Patent 11 1 1111 3,788,748 Knight et al. Jan. 29, 1974INDICATING THE PASSING OF A 3,581,099 5/1971 Franke 350/191 PRO THRQUGHAN AREA IN 3,619,630 1l/l97l McLeod et a] 1 1 250/222 R SPACE 3,624,40111/197] Stoiler 250/222 R 3,401,937 9/1968 Rockwood et al. 250/222 R[75] Inventors: Lindsay Charles Knight; Colin ,475,029 10/ 1969 Hyman250/222 R Maxwell Finch both of Allyn-y 3,597,755 8/l97l Parkin i l i 1340/258 B S w Noel Harry Fred W d 3,554,646 l/l97l Carlson 1 1 1 1 1 i1 1. 356/4 3,134,975 5/1954 Goodman 1. 543/11 g a g bgzrg fig Albury3,512,888 5 1970 Humphrey 3,603,998 9/i97l Kassel [73] Assignee:Australasian Training Aids $120,654 2/ 964 Lee proprietor Limited,Albury New 3,678,492 7/i972 Casper 340/258 B South Wales, Australia 22Filed; Jan. 2 72 Primary Exam1'nerBenjamin A. Borchelt AssistantExaminer-S. C. Buczinski [2]] Appl 219,366 Attorney, Agent, orFirm-Oberlin, Maky, Donnelly &

Renner [30] Foreign Application Priority Data J .2l,l97l A t l' ..3775

[57 ABSTRACT [52] Cl 356/141 356/4 g A method of and apparatus forindicating the passing l 1 Int Cl G0") "/26 of a projectile through anarea in space comprising in ciding the whole of Said area with aprojectile light [58] Field of 32 5,: f; g beam and detecting areflection of said beam off a projectile passing through said arearesulting from incidence of said beam thereon thereby determining [56]UNlTE S :ZqrENTS that said projectile passed through said area.

3,6I5,l35 10 1971 Frazer 356/5 29 Claims, 10 Drawing Figures 8 I I I 1 1l f r 1 {1 g 4 2 l 1 1 I l /l L 5 PATENTEDmzsmm 3.788 748 sum 1 BF 4PATENTEUJM 2 9 $974 3. 788.748

sum 2 0f 4 DIREC T ION OF PROJECT/LE memo/v jg. 6. OFPRUJECTILEPATENTEDJAHZBISM 3 788.748

SNEEI 3 Bi 4 DC A DC/NPUT 4 REG 103 ""51 If E BPF 05a 9 ourrur DET :---'1 f 1 g Fla/v01 AND2 FAND3 i swvc I r I v l I .STORE 7 I REC CLOCKTRANS TATENTEUJM 29 2974 3.788.748

sum u or 4 NAV/ COMM STORE DECODE MIM RANGE LOWER LIMIT MAX. RANGE UPPERLIMIT INDICATING THE PASSING OF A PROJECTILE THROUGH AN AREA IN SPACEBACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates to indicating the passing of a projectile through an area inspace.

The invention has particular application in determin ing accuracy of aimof bullets, cannon shells, missiles and the like at a target and hasparticular application in air-to-air and air-to-ground gunnery.

2. Description of Prior Art Hitherto it has been necessary to visuallyinspect towed drogue targets after shooting thereat by an attackingaircraft. The count of hits determined by that inspection can then beradioed to the attacking aircraft. The time taken for the visualinspection is considerable and as we are here considering militaryaircraft which are expensive to keep in the air the cost of the visualinspection is considerable.

The object of this invention is to provide a method of, and apparatusfor, indicating the passing of a projectile through a target area inspace which can be applied to gunnery generally and specifically, butnot exclusively, to air-to-air and air-to-ground gunnery.

BRIEF SUMMARY OF THE INVENTION The present invention provides a methodof indicating the passing of a gunnery projectile through an area inspace comprising inciding the whole ofsaid area with a projected lightbeam and detecting a reflection of said beam off a gunnery projectilepassing through said area resulting from incidence of said beam thereonthereby determining that said projectile passed through said area. Theterm gunnery projectile" as used herein is intended to include allprojectiles fired or projected from military or civilian firing orprojecting equipment such as guns, pistols, rifles, rocket launchers,and missle launchers. and wherein the projectiles have a relatively highvelocity as compared to projectiles such as stones thrown or fired byslingshots or arrows fired by bows or like type weapons.

This invention also provides gunnery apparatus for use in gunnerycomprising a light beam projector adapted to incide the whole of an areain space with a projected light beam produced by said projector and adetector adapted to detect a reflection of said beam off a gunneryprojectile passing through said area resulting from incidence of saidbeam thereon thereby to determine that said projectile passed throughsaid area.

This invention further provides a method of indicating the passing of agunnery projectile through one of a number of areas in space comprisingscanning said areas with one or more projected light beams such that oneof said one or more beams will incide on a projectile passing throughone of said areas and detecting a reflection of said one of said one ormore beams off said projectile resulting from such incidence anddetermining from which of said areas said reflection originated therebydetermining that said projectile passed through said one of said areasfrom which said reflec tion originated.

This invention further provides gunnery apparatus for indicating thepassing of a projectile through one of a number of areas in spacecomprising scanning means adapted to scan said areas with one or moreprojected light beams such that one of said one or more beams willincide on a projectile passing through one of said areas, and a detectoradapted to detect a reflection of said one of said one or more beams offsaid projectile resulting from such incidence and to determine fromwhich otsaid areas said reflection originated thereby to determine thatsaid projectile passed through the one of said areas from which saidreflection originated.

According to a still further aspect of this invention there is provideda lens comprising a slab of light transmitting material having twosubstantially straight edges which converge and having a part, adjacentthe apex defined by said edges, adapted to diverge light entering thelens thereat and wherein said edges are reflective to light within theslab whereby, when in use, said lens is adapted to produce a fan shapedbeam of angle equal to the angle included by said edges.

According to a further aspect of the invention there is provided areflector comprising a body. a number of reflecting surfaces on asurface of the body around a central axis thereof, said reflectingsurfaces being disposed so that when a beam of light is directed at oneof the surfaces and the body is rotated about the central axis, the beamoflight will be reflected successively by each reflector surface to scanan area in space, the rcflecting surfaces being so shaped and arrangedso that at the instant of completion of scan from one reflecting surfacethe beam is caused to again start scanning the area in space.

Preferred aspects and details of the present invention will now bedescribed with the aid of the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic representationof an optical part of an apparatus in accordance with the presentinvention.

FIG. 2 is a schematic representation of a different version of theoptical part of the apparatus shown in FIG. I.

FIG. 3 is a perspective view of a lens used in the apparatus shown inFIG. 1.

FIG. 4 is a perspective view of a reflector used in the apparatus shownin FIG. 2.

FIG. 5 is an end view of the reflector shown in FIG. 4.

FIG. 6 is a representation of an area incided with light by theapparatus shown in FIGS. 1 and 2.

FIGS. 7, 8 and 9 are block circuit diagrams of appa ratus forming anelectronic part of the present invention.

FIG. 10 is a cross sectional view of a bird and drogue in which bird theapparatus shown in FIG. I and 2 may be fitted and towed behind anaeroplane.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1 the opticalpart of the apparatus has a continuous wave helium-neon laser 1.

A beam 2 generated by the laser 1 is directed onto an inclined quartzmirror 3 which has a mirror coating on the second surface, relative tobeam 2, such that between approximately of beam 2 is transmittedtherethrough to be beam 4. Beam 4 is passed into a lens 5. The lens 5 isshaped as a segment of a circle cut from a sheet of perspex (see FIG. 3)and beam 4 is directed to bisect the angle of the segment and passescentraliy thereinto at a circular cut-out portion 6. Cutout portion 6causes beam 4 to project as beam 8 which can for convenience be calledthe incident beam" which is of substantially rectangular cross sectionas shown by dotted line without substantial transverse divergence.

The lens 5 comprises a generally triangular slab of light transmittingmaterial having two substantially straight edges which converge, andhaving a part in the form of a part cylindrical notch 6 adjacent to apexdefined by the converging edges, which is adapted to diverge lightentering the lens at the apex. The two straight edges of the lens, notbeing the edge opposite the apex at which light is to enter the lens,are reflective to light within the lens. For example, the edges may bemirrored. Such a lens is adapted to produce a fan shaped beam of lighthaving an angle which is equal to the angle included by the edges of theslab adjacent the apex at which light is to enter the slab.

If a projectile such as a bullet or cannon shell should pass throughbeam 8 it will be incided by beam 8. Since the projectile cannot be aperfect black body, a portion of the beam will be reflected thereby, anda portion of that reflection, conveniently known as the reflected beam,will return to lens 5 where it will be collected and directed at mirror3 as beam 9. Beam 9 will be reflected by mirror 3 which is first surfacecoated, with respect thereto, as beam 10. The coating of mirror 3 issuch that beam 10 will be approximately 50 percent of beam 9. Beam 10passes through an optical band pass filter 12 which prevents light offrequency substantially different to that of laser 1 from passing so asto reduce errors which may arise from stray light such as sunlight. Beaml0 emerges as beam 13 which then passes through lens 14 which focusesbeam 13 onto the centre of PIN diode 15. PIN diode 15 thus emits anelectrical signal represented as 17. Signal 17 will be hereinafterreferred to as the reflected signal. The optical part ofthe apparatusdescribed with respect to FIG. 1 provides an indication of a projectilepassing through beam 8 and can be used, as to be described later, togive an indication of accuracy of shooting at a target.

As lens 5 is shaped primarily for projecting beam 4 as beam 8 and notfor receiving the reflected beam off a projectile and causing that beamto be beam 9 a fun ther lens shaped primarily for receiving thereflected beam may be provided and placed at a suitable locationadjacent lens 5 to receive a reflected beam when it reflects along anaxis to one side of the axis of projecting beam 8.

Referring now to FIG. 2, which shows a different ver sion of an opticalpart of the apparatus, there is provided a helium-neon laser 21 whichgenerates a continuous wave laser beam 22. The beam 22 generated by thelaser is directed onto an inclined quartz mirror 23 first surfacecoated, relative to beam 22, which has a mirror coating such thatbetween I and 5 percent of the beam 22 is reflected thereby to be beam24 and between 95 percent and 99 percent of the beam 2 passestherethrough to be beam 26.

Beam 26 is directed onto an inclined quartz mirror 27 second surfacecoated, relative to beam 26, and approximately 50 percent of beam 26passes therethrough to be beam 28.

Beam 28 then passes to a faceted reflector 29 and is reflected therebyto be beam 31.

The reflector 29 comprises a rectangular body 32 which is rotated abouta face centred axis on shaft 33 by motor 34. Also fixed to the shaft isa disc 36. On the body 32, see FIGS. 4 and 5, are four planar mirrorsurfaces. The mirrors are disposed at relative to one another on thesides of the body 32.

It is to be noted that said axis is at right angles to beam 28 but forconvenience of depiction is shown in line therewith in FIG. 2.

Prior to passing to body 32 beam 28 is passed through a lens 5 similarto that described in respect of FIG. 1 see FIGS. 4 and 5.

As a result of rotation of the body 32 the beam 28 is reflected, inturn, by each of the mirrors to be, as stated before, beam 31. Beam 31as a result of rotation of the body 32 scans an area, hereinafter called"the scanned area." The scanned area has the shape shown in FIG. 6.

As a result of lens 5 the beam 31 has an elongated section 37 as shownin FIG. 2 and FIG. 6.

The shape of the scanned area is as shown in FIG. 6 and the reflectorcauses beam 31 to be of elongated section 37 as aforesaid and outwardlydiverging as shown and scanning a segment. A lower limit as far asoperation of the apparatus is concerned is arbitrarily set and an upperlimit as far as operation of the apparatus is concerned is arbitrarilyset in an electronic part of the invention. The depth ofthe beam to aprojectile at the lower limit of scan is conveniently 27 inches for oneparticular embodiment, although it will be understood that the lowerlimit may be considerably greater in particular applications, forexample, air to air targets.

The angular velocity of the body 32 and the width of the beam 31(measured along the long and short axes of said elongated section 37)are chosen so that a projectile such as a bullet passing through thescanned area will be incided by beam 31.

For a projectile speed of 4,000 ft/sec. the time to travel through thebeam, for the depth of the beam to the projectile of 27 inches at thelower limit of intended scan. (27/48) m.sec. 0.564 m.sec.

Thus for a 4 sided body 32 the speed of rotation of the body 32 isdesirably not less than WOO/0.564 X 4) 443 Revs/sec 26580 RPM. Inpractise we have found it best for these dimensions to be in excess ofthat required so as to be applicable to a wide range of projectilevelocities.

If a projectile such as a bullet or cannon shell should pass through thescanned area it will be incided by the beam 31. Beam 31 is convenientlycalled the incident beam. Since the projectile cannot be a perfect blackbody, perfect 3] will be reflected thereby and a portion of thereflection will travel back along the path of beam 31 at the instant ofincidence. That portion will be known as beam 38 and it is convenient torefer to it as the reflected beam" and it will be realised that the beam38 will have the nature of a pulse and not be continuous.

Beam 38 is reflected by the mirrors on body 32 and will travel along thepath of beam 28, except that it will travel in the opposite direction,as beam 19.

Beam 19 meets mirror 27 which. to beam 39 is first surface coated, andapproximately 50 percent reflected thereby as beam 41.

Beam 41 then passes to optical band pass filter 42 which prevents lightof frequency substantially different to that of the laser from passingso as to reduce errors which may arise from stray light such assunlight.

From filter 42 beams 43 emerges and passes to a PIN diode 44. The beam43 causes the diode 44 to emit an electrical signal which is representedas 46. That signal will be hereinafter called the reflected signal,"

Beam 24 is passed to inclined mirror 47 and is substantially entirelyreflected thereby to be beam 48. Beam 48 passes through lens system 49and emerges as beam 51.

The disc 36 has a large number of optical holes of apertures adjacentits periphery with their centres at the same radial distance from thecentre of rotation of the disc. The holes are arranged in four groupsand the groups are angularly disposed relative to one another in thesame manner as the four mirrors on body 32 are angularly disposedrelative to one another. Each group corresponds to one of the fourmirrors so that whilst one mirror is reflecting beam 38 the groupcorresponding to that mirror is disposed so that beam 51 is passingthrough the holes in that group to emerge from the disc as pulse beams52.

Pulse beams 52 pass to PIN diode 53 and cause the diode 53 to emit apulsed electric signal which is represented as 54. That signal will behereinafter called the reference pulse signal."

In use the apparatus is set up so that the scanned area will begenerally along the sides of a target or other convenient objects to aimat. The invention. of course, has particular application in air-to-airand airto-ground gunnery and in which case the scanned area will be infront ofa towed drogue as shown in FIG. 10, or in front of or behind aground target.

Referring now to FIG. 10, when the apparatus is to be used in air to-airgunnery a bird 60 is connected at one end by a tow line 61 to anaircraft and connected at the other end by a tow line 62 to a drogue 63.The optical part of the invention is shown as a block 64 and is arrangedsuch that the incident beam produced by it is in a vertical planeadjacent drogue 63.

If the optical part of the apparatus as described with respect to FIG. 1is used in the bird 60 then the lens 5 thereof is arranged so that theincident beam thereof is as shown by lines 6667.

If the optical part of the apparatus as shown in FIG. 2 is used in thebird 60 the mirror surfaces can be arranged to cause the angle of scanof the beam to be as shown by lines 66-67 but preferably they arearranged to cause the scan to be as shown between lines 68-69 and with aminimum and maximum ranges as shown with respect to the drogue 63.

At the end of a days shooting the drogue 60 can be hauled in to theaircraft or the tow line 61 can be released from the aircraft and aparachute in the bird 60 made operable as a consequence of releasingtowline 61 so that the bird can be safely landed.

It will be realised that the optical part of the apparatus can bemounted in the aircraft instead of in the bird for air-to-air gunnerybut because the drogue is towed a considerable distance behind theaircraft so as to avoid the towing aircraft from being hit byprojectiles and for economy of laser constructions and efficiencyofoperation of the apparatus we prefer the optical part of the apparatusto be as close as possible to the target so the magnitude of reflectionof the laser beam will be as large as possible.

In air-to-ground gunnery the optical part of the apparatus is arrangedto produce the incident beam in front of the target as is shown in FIG.6.

Manners in which the reflected signal and the reference pulse signal canbe used will now be generally described and thereafter circuitry used toderive information from those signals will be described in detail.

Since the reflected signal is a pulsed signal the number of projectilespassing through the scanned area is determined merely by counting thepulses. By this means a crude estimation of aim accuracy is obtainable.

Further, since the reflected signal will have a magnitude related to themagnitude of the reflected beam and, since the magnitude of thereflected beam is related to the distance ofthe projectile on which theincident beam incided, it is possible, by rejecting signals of below orabove predetermined magnitudes, to put an upper limit and a lower limiton the range at which projectiles will be detected. These ranges areshown in FIGS. 6 and 10. It will be realised that this provides a betterestimation of aim accuracy. Further increase in quality of estimationcan be obtained by determining the relation of the magnitude ofthereflected signal to range of projectiles but it will be realised thatsuch a relation is likely to vary substantially dependent on whether thereflected signal is obtained from relatively large or relatively smallcalibre projectiles.

By the use of the optical part of the apparatus as shown in FIG. 2 withthe aid of other means it is possible to determine the angular position,relative to an imaginary baseline, of a detected projectile in thescanned area. This is done by providing a certain aper ture in said disclarger than the other apertures. Said certain aperture will produce apulse in the reference pulse signal larger and longer than the pulseproduced by the other apertures. Said certain aperture is alsopositioned so that the pulse produced thereby is pro duced at theinstant that one of the mirrors commences to scan the scanned area. Byknowing the number of pulses produced during the time that said one ofthe mirrors is scanning the scanned area and by dividing that number byanother number conveniently, three it is possible. by counting pulsesand relating the reflected signal to the count at the time that thereflected signal is received to determine the angular position, relativeto an imaginary base line. of a projectile in the scanned area in threesegments of the scanned area. Thus an even more accurate estimation ofaim accuracy is obtained.

The above is a general description of manners of using the pulsereference signal and the reflected signal. More specific details andcircuitry used in a preferred instance is given below.

The circuit used for obtaining signals corresponding to a projectilepassing within a certain range of the ori gin of the incident beam isshown in FIG. 7 and includes a PIN diode (previously referred to bynumber as 15 and 44). When a reflected light beam off a projectilestrikes PIN diode a signal is generated which is now indicated by I00.The signal I00 is fed to a band pass filter B.P.F. arranged with circuitconstants to only allow a signal falling within a predetermined range offrequencies to pass. The signal passed from the band pass filter isshown generally as 102. The signal 102 is amplified by a radio frequencyamplifier RF. and clamped by a level set and detected between presetlevels to generate an output shape shown generally as 103. The signalI03 is used to trigger an oscillator to generate a signal, showngenerally as 104 of known duration and amplitude. A DC. regulator isused for supplying constant voltage to the above circuit integers.

When using the optical part of the apparatus as shown in FIG. 1 thesignal 104 can be fed directly into a store. This is shown basically inFIG. 8 except that ad ditional circuitry outlined with dotted lines isshown. The additional circuitry will be explained later. On the receiverREC receiving a command signal or after a fixed small time delay afterthe first detected hit in a burst the STORE is made operative to feedinformation stored therein in binary code on signals from CLOCKconcerning hits to a transmitter TRANS which in turn transmits theinformation to be received by an aircraft firing at the drogue or groundtarget. The transmitter TRANS operates at a frequency such that theusual NAV/COMM equipment in the aeroplane can receive the information.This is basically shown in FIG. 9 except that further additionalcircuitry is shown. The further additional circuitry will be explainedlater. Connected to the NAV/COMM equip ment is a decoder DECODE whichdecodes the information received and feeds it to a display unit DIS-PLAY which has a series of digital reading display tubes for giving anindication of the number of projectiles which passed through theincident beam and hence the number of target hits.

The receiver REC in the circuitry shown in FIG. 8 is made operative onreceipt of a command signal from the transmitter in the NAV/COMMequipment of the aircraft which is shooting at the target. The commandsignal can be initiated by the pilot or gunner in the aircraft.Alternatively, the transmission of hit data may be made automatic aftera small time delay seconds).

When the optical apparatus shown in FIG. 2 is used the signal 104 ispreferably fed to three electronic gates, AND 1, AND 2 and AND 3, (seeFIG. 8) which gates are individually openable for a period correspondingto a number of selected reference pulse signals. The selected referencepulse signals are obtained by providing suitable dividing means fordividing the pulse signals generated by the number of apertures in thedisc 36 into groups of signals and using those signals to operatefurther circuit means to generate a signal to open a gate for theduration of each group of sig nals. The disc 36 has l,l99 equally spacedcircumferential apertures and one larger circumferential aper ture,totalling 1.200 apertures. The larger aperture is aligned to correspondto the start of scan of the beam across the scanned area by one of themirrors. Because there are four mirrors there are I,200/4) 300 aperturescorresponding to each mirror. By providing dividing means for counting300/3 100 pulses and means for generating a signal to be fed to one ofthe three gates for the duration of I00 pulses and. to a second of thethree gates for the duration of the next IOO pulses and, to a thirdofthc three gates for the next I00 pulses. from the SYNC and back to thesaid one of the gates for the next 100 pulses. etc., we can open each ofthe gates for a third of the sector of scan of the beam. In the presentcase the area of scan is divided into three sectors. As the signal 104is fed to all three gates, it passes only through the gate which isopened. Hence we can obtain a signal representative of which sector aprojectile passed through. and hence we can obtain a more accuratedetermination of the accuracy ofthe air of the projectile. The threegates may correspond to Left of target," Hit target, and Right oftarget" respectively. The hit information from the gates is fed into theSTORE and transmitted as described for the optical construction shown inFIG. 1.

The hit information transmitted by TRANS is re ceived by the NAV/COMMequipment shown in FIG. 9 and fed into a STORE from the STORE theinformation is fed to a decode which decodes the information which is inbinary form into a suitable form for operating a display unit. Thedecoded information is fed to a display unit DISPLAY where it can beread by an observer.

It will be appreciated that by using the apparatus as described above itis possible for a number of aircraft to fire at a target, one at a time,and for an indication of the accuracy of shooting at the target to begiven almost instantaneously to each aircraft in turn. Hence the cost ofkeeping several aircraft in flight whilst manu ally counting the hits ofthe target is reduced.

In order to eliminate the effect of sunlight or effects of other lightbeams or effects of slow moving objects passing through the incidentbeam from being registered as hits the circuitry used for registering ahit re sulting from a projectile passing through the incident beam maybe arranged to operate when a projectile leaves the scanned area, byproviding a blanking signal to a reflected signal which occurs for, sayevery three scans of light beam.

In order to reduce the diameter of disc 36 having re gard to theproblems involved in producing a required number of apertures at theperiphery thereof as the disc becomes smaller and smaller in diameterthe disc can be provided with magnetic signals of differing fre quencyand having a relation to the number of apertures which would otherwisebe used. A tape recording replay head can be arranged to read therecorded sig nals as the disc 36 rotates so that signal 54 can begenerated and used as previously described.

To ensure that a hit is not registered in two sectors of scan if aprojectile passes through the transition po sition of two adjacentsectors ofscan. tl'tc reflected signal can be used to inhibit the nextcount until after a set time.

Throughout the specification the term light beam has been used and thisis to be understood to include light which is visible and light which isnot visible. The term light beam is to include light which is in the IR.spectrum and light which is in the UV. spectrum.

We claim:

1. A method of indicating the passing of a gunnery projectile through anarea in space comprising inciding the whole of said area with aprojected light beam which passes through a lens element so as toprovide a fan shaped beam which at least partially defines said area inspace, and detecting a reflection of said beam offa projectile passingthrough said area resulting from incidence of said beam thereon therebydetermining that said projectile passed through said area, saidreflected beam passing through said lens element prior to saiddetection.

2. A method claimed in claim I, wherein said beam is ofa size. in use,such as to incide the whole of said area and is stationary.

3. A method as claimed in claim I, wherein said beam is ofa length inthe direction of intended movement of a gunnery projectile insufficientto incide the whole of said area and is scanned such that said beamincides the whole of said area and such that said beam will incide aprojectile passing through said area.

4. A method as claimed in claim 3, further including the step ofrelating said reflection to the angular position of said beam at thetime of detecting said reflection whereby to derive information on theangular position of said projectile.

S. The method of claim 4, further including the step of disregardingreflections of said beam offa projectile above and below predeterminedmagnitudes whereby to define boundaries of said area.

6. A method as claimed in claim 1 wherein said beam is fan shaped.

7. A method as claimed in claim 1 wherein said beam is generated by alaser.

8. Gunnery apparatus for indicating the passing of a gunnery projectiletravelling at a relatively high speed originating from a weaponcomprising a light beam projector adapted to incide the whole of an areain space with a projected light beam produced by said projector, a lenselement in the path of said projected beam to produce a fan shaped beamat least partially defining said area in space, and a detector adaptedto detect a reflection of said beam off said gunnery projectiletravelling at a high speed through said area, whereby said reflectionresults from incidence of said beam thereon thereby to determine thatsaid projectile passed through said area, and said reflected beam passesthrough said lens element to said detector.

9. Gunnery apparatus as claimed in claim 8 wherein said projector issuch that said beam is ofa size, in use, such as to incide the whole ofsaid area and is stationary.

l0. Gunnery apparatus as claimed in claim 9 wherein said projector issuch that said beam is ofa size and of a length in the direction ofintended movement of a gunnery projectile insufficient to incide thewhole of said area, and further comprising scanning means adapted toscan said beam such that said beam incides the whole of said area andsuch that said beam will incide a gunnery projectile passing throughsaid area.

ll. The gunnery apparatus of claim 10, further including a reflectivesurface mounted for movement whereby to scan said area with a light beamreflected therefrom such as to incide a gunnery projectile pass ingthrough said area.

12. The gunnery apparatus of claim 11, further including means adapted,in use, to produce an indicia of the angle said beam makes with respectto a reference line at any one time,

13. Gunnery apparatus as claimed in claim 8, further including meansadapted to produce a visual or audible signal consequent on detection ofsaid reflection by said detector.

14. Gunnery apparatus as claimed in claim 8, further including meansadapted to relate said reflection to the angular position of said beamat the time of detecting said reflection by said detection whereby toprovide information on the angular position of said projectile.

l5. Gunnery apparatus as claimed in claim 8, further including meansadapted to disregard reflection of said beam off a gunnery projectileabove and below predetermined magnitudes whereby to define boundaries ofsaid area.

16. A method of indicating the passing of a gunnery projectile throughone of a number of areas in space comprising scanning said areas with aprojected light beam such that said beam will incide on said projectilepassing through one of said areas, and detecting a reflection of saidbeam off said projectile and determining from which of said areas saidreflection originated thereby determining that said projectile passedthrough said one of said areas from which said reflection originated.

17. A method as claimed in claim 16, wherein said beam is caused to scansaid areas by reflecting off a reflector moving with respect to saidbeam before it is projected.

18. A method as claimed in claim 16 wherein an electrical signal isgenerated when said reflection is detected and wherein an electricalreference signal is generated representative of the one of said areasbeing scanned by said beam at any one time and wherein the firstmentioned electrical signal is related with the electrical referencesignal to provide an indication of which of said areas the projectilepassed through.

19. A method as claimed in claim 18, wherein information related to thefirst mentioned electrical signal and the electrical reference signal istransmitted to a display unit and displayed as an indication of aprojectile which passed through the respective area.

20. Gunnery apparatus for indicating the passing of a projectiletravelling at a relatively high speed originating from a weapon andindicating the passing of a projectile through one of a number of areasin space, comprising scanning means adapted to scan said areas with aprojected light beam such that said beam wiil incide on a projectiletravelling at high speed through one of said areas, and a detectoradapted to detect a reflection of said beam off said projectileresulting from such incidence and to determine from which of said areassaid reflection orignated thereby to determine that said projectilepassed through the one ofsaid areas from which said reflectionoriginated.

2l. Gunnery apparatus as claimed in claim 20 further including meansadapted to produce an electrical signal consequent on detection of saidreflection, means adapted to produce an electrical reference sigrialrepresentative of the one of said areas being scanned by said beam atany one time and including means adapted to relate the first mentionedsignal to the electrical reference signal to provide an indication ofwhich of said areas said projectile passed through.

22. Gunnery apparatus as claimed in claim 21, further including a numberof electronic gates selectively operable by the electrical referencesignal whereby each of said gates represents one of said areas and isopen when said beam is scannning the respective one of said areas andwherein circuitry is provided adapted to feed the first mentionedelectrical signal to said gates whereby passage of the first mentionedelectrical signal through one of said gates indicates which of saidareas said projectile passed through.

23. A lens comprising a slab of light transmitting material having twosubstantially straight edges which converge and having a part, adjacentthe apex defined by said edges, adapted to diverge light entering thelens thereat and wherein said edges are reflective to light within theslab whereby, in use, said lens is adapted to produce a fan-shaped beamof angle equal to the angle included by said edges.

24. A lens comprising a generally triangular slab of light transmittingmaterial having a part adjacent one of apexes thereof adapted to divergelight entering the lens thereat and wherein the edges of the lens otherthan the edge opposite said part are reflective to light within the slabwhereby, in use, said lens is adapted to produce a fan-shaped beamhaving an angle equal to the angle included by the edges adjacent saidpart.

25. A lens as claimed in claim 24 wherein said part comprises a partcylindrical notch.

26. Apparatus for indicating the presence of a gunnery projectiletravelling at a relatively high speed originating from a weapon in anarea in space, comprising a light beam projector for projecting acontinuous beam of light, a lens element in the path of said continuousprojected beam, said lens element having a concavity in the end thereofreceiving said projected beam, said concavity serving to convert saidcontinuous beam into an incident beam having a width proportional tosaid concavity, thereby to define said area in space, a reflector forreceiving a reflected beam off a projectile in said area resulting fromincidence of said projected beam thereon, and a detector adapted todetect said reflected beam thereby to determine the presence of saidprojectile.

27. Apparatus for indicating the presence of a gunnery projectile in anarea in space, comprising light beam projector, said projector includinga reflector element for reflecting a beam of light so as to incide thewhole of said area in space with a projected light beam produced by saidprojector, said reflector element being movably mounted and furtherincluding a lens element in the path of the projected light beam andpositioned between said beam projector and said reflector element, saidlens element having a concavity in the end thereof receiving saidprojected beam, said concavity serving to convert said continuous beaminto an incicent beam having a width proportional to said concavity,said incident beam being reflected by said movable reflector element toscan the whole of said area in space, and a detector adapted to detect areflection of said beam offa projectile in said area resulting fromincidence of said beam thereon, the energy reflected by the projectilebeing directed to said detector by said reflector element thereby todetermine the presence of said projectile.

28. The apparatus of claim 27 wherein said reflector element comprises afour-sided member having planar reflecting surfaces at each side, meansfor mounting said reflector element on an axis perpendicular to the axisof said lens element, and means for rotating said reflector element at asufficiently high speed so as to substantially continuously incide saidarea in space so as to detect the presence of a projectile travelling ata predeterminedly known speed.

29. Gunnery apparatus for indicating the passing of a projectiletravelling at a relatively high speed originating from a weapon,comprising means for projecting a light beam, scanning means adapted toscan a defined area in space with said projected light beam such thatsaid beam will incide on a projectile travelling at such high speedpassing through said area, and a detector adapted to detect a reflectionof said beam off said projectile resulting from such incidence and todetermine that said projectile passed through said area.

1. A method of indicating the passing of a gunnery projectile through anarea in space comprising inciding the whole of said area with aprojected light beam which passes through a lens element so as toprovide a fan shaped beam which at least partially defines said area inspace, and detecting a reflection of said beam off a projectile passingthrough said area resulting from incidence of said beam thereon therebydetermining that said projectile passed through said area, saidreflected beam passing through said lens element prior to saiddetection.
 2. A method as claimed in claim 1, wherein said beam is of asize, in use, such as to incide the whole of said area and isstationary.
 3. A method as claimed in claim 1, wherein said beam is of alength in the direction of intended movement of a gunnery projectileinsufficient to incide the whole of said area and is scanned such thatsaid beam incides the whole of said area and such that said beam willincide a projectile passing through said area.
 4. A method as claimed inclaim 3, further including the step of relating said reflection to theangular position of said beam at the time of detecting said reflectionwhereby to derive information on the angular position of saidprojectile.
 5. The method of claim 4, further including the step ofdisregarding reflections of said beam off a projectile above and belowpredetermined magnitudes whereby to define boundaries of said area.
 6. Amethod as claimed in claim 1 wherein said beam is fan shaped.
 7. Amethod as claimed in claim 1 wherein said beam is generated by a laser.8. Gunnery apparatus for indicating the passing of a gunnery projectiletravelling at a relatively high speed originating from a weaponcomprising a light beam projector adapted to incide the whole of an areain space with a projected light beam produced by said projector, a lenselement in the path of said projected beam to produce a fan shaped beamat least partially defining said area in space, and a detector adaptedto detect a reflection of said beam off said gunnery projectiletravelling at a high speed through said area, whereby said reflectionresults from incidence of said beam thereon thereby to determine thatsaid projectile passed through said area, and said reflected beam passesthrough said lens element to said detector.
 9. Gunnery apparatus asclaimed in claim 8 wherein said projector is such that said beam is of asize, in use, such as to incide the whole of said area and isstationary.
 10. Gunnery apparatus as claimed in claim 9 wherein saidprojector is such that said beam is of a size and of a length in thedirection of intended movement of a gunnery projectile insufficient toincide the whole of said area, and further comprising scanning meansadapted to scan said beam such that said beam incides the whole of saidarea and such that said beam will incide a gunnery projectile passingthrough said area.
 11. The gunnery apparatus of claim 10, furtherincluding a reflective surface mounted for movement whereby to scan saidarea with a light beam reflected therefrom such as to incide a gunneryprojectile passing through said area.
 12. The gunnery apparatus of claim11, further including means adapted, in use, to produce an indicia ofthe angle said beam makes with respect to a reference line at any onetime.
 13. Gunnery apparatus as claimed in claim 8, further includingmeans adapted to produce a visual or audible signal consequent ondetection of said reflection by said detector.
 14. Gunnery apparatus asclaimed in claim 8, further including means adapted to relate saidreflection to the angular position of said beam at the time of detectingsaid reflection by said detection whereby to provide information on theangular position of said projectile.
 15. Gunnery apparatus as claimed inclaim 8, further including means adapted to disregard reflection of saidbeam off a gunneRy projectile above and below predetermined magnitudeswhereby to define boundaries of said area.
 16. A method of indicatingthe passing of a gunnery projectile through one of a number of areas inspace comprising scanning said areas with a projected light beam suchthat said beam will incide on said projectile passing through one ofsaid areas, and detecting a reflection of said beam off said projectileand determining from which of said areas said reflection originatedthereby determining that said projectile passed through said one of saidareas from which said reflection originated.
 17. A method as claimed inclaim 16, wherein said beam is caused to scan said areas by reflectingoff a reflector moving with respect to said beam before it is projected.18. A method as claimed in claim 16 wherein an electrical signal isgenerated when said reflection is detected and wherein an electricalreference signal is generated representative of the one of said areasbeing scanned by said beam at any one time and wherein the firstmentioned electrical signal is related with the electrical referencesignal to provide an indication of which of said areas the projectilepassed through.
 19. A method as claimed in claim 18, wherein informationrelated to the first mentioned electrical signal and the electricalreference signal is transmitted to a display unit and displayed as anindication of a projectile which passed through the respective area. 20.Gunnery apparatus for indicating the passing of a projectile travellingat a relatively high speed originating from a weapon and indicating thepassing of a projectile through one of a number of areas in space,comprising scanning means adapted to scan said areas with a projectedlight beam such that said beam will incide on a projectile travelling athigh speed through one of said areas, and a detector adapted to detect areflection of said beam off said projectile resulting from suchincidence and to determine from which of said areas said reflectionorignated thereby to determine that said projectile passed through theone of said areas from which said reflection originated.
 21. Gunneryapparatus as claimed in claim 20 further including means adapted toproduce an electrical signal consequent on detection of said reflection,means adapted to produce an electrical reference signal representativeof the one of said areas being scanned by said beam at any one time andincluding means adapted to relate the first mentioned signal to theelectrical reference signal to provide an indication of which of saidareas said projectile passed through.
 22. Gunnery apparatus as claimedin claim 21, further including a number of electronic gates selectivelyoperable by the electrical reference signal whereby each of said gatesrepresents one of said areas and is open when said beam is scannning therespective one of said areas and wherein circuitry is provided adaptedto feed the first mentioned electrical signal to said gates wherebypassage of the first mentioned electrical signal through one of saidgates indicates which of said areas said projectile passed through. 23.A lens comprising a slab of light transmitting material having twosubstantially straight edges which converge and having a part, adjacentthe apex defined by said edges, adapted to diverge light entering thelens thereat and wherein said edges are reflective to light within theslab whereby, in use, said lens is adapted to produce a fan-shaped beamof angle equal to the angle included by said edges.
 24. A lenscomprising a generally triangular slab of light transmitting materialhaving a part adjacent one of apexes thereof adapted to diverge lightentering the lens thereat and wherein the edges of the lens other thanthe edge opposite said part are reflective to light within the slabwhereby, in use, said lens is adapted to produce a fan-shaped beamhaving an angle equal to the angle included by the edges adjacent saidpart.
 25. A lens as claimed in cLaim 24 wherein said part comprises apart cylindrical notch.
 26. Apparatus for indicating the presence of agunnery projectile travelling at a relatively high speed originatingfrom a weapon in an area in space, comprising a light beam projector forprojecting a continuous beam of light, a lens element in the path ofsaid continuous projected beam, said lens element having a concavity inthe end thereof receiving said projected beam, said concavity serving toconvert said continuous beam into an incident beam having a widthproportional to said concavity, thereby to define said area in space, areflector for receiving a reflected beam off a projectile in said arearesulting from incidence of said projected beam thereon, and a detectoradapted to detect said reflected beam thereby to determine the presenceof said projectile.
 27. Apparatus for indicating the presence of agunnery projectile in an area in space, comprising light beam projector,said projector including a reflector element for reflecting a beam oflight so as to incide the whole of said area in space with a projectedlight beam produced by said projector, said reflector element beingmovably mounted and further including a lens element in the path of theprojected light beam and positioned between said beam projector and saidreflector element, said lens element having a concavity in the endthereof receiving said projected beam, said concavity serving to convertsaid continuous beam into an incicent beam having a width proportionalto said concavity, said incident beam being reflected by said movablereflector element to scan the whole of said area in space, and adetector adapted to detect a reflection of said beam off a projectile insaid area resulting from incidence of said beam thereon, the energyreflected by the projectile being directed to said detector by saidreflector element thereby to determine the presence of said projectile.28. The apparatus of claim 27 wherein said reflector element comprises afour-sided member having planar reflecting surfaces at each side, meansfor mounting said reflector element on an axis perpendicular to the axisof said lens element, and means for rotating said reflector element at asufficiently high speed so as to substantially continuously incide saidarea in space so as to detect the presence of a projectile travelling ata predeterminedly known speed.
 29. Gunnery apparatus for indicating thepassing of a projectile travelling at a relatively high speedoriginating from a weapon, comprising means for projecting a light beam,scanning means adapted to scan a defined area in space with saidprojected light beam such that said beam will incide on a projectiletravelling at such high speed passing through said area, and a detectoradapted to detect a reflection of said beam off said projectileresulting from such incidence and to determine that said projectilepassed through said area.